Panels or sheets made of polymethyl-methacrylate (PMMA), also known as acrylic glass, are commonly used in acoustic barriers due to their transparency, weather resistance, and noise abatement properties. Such acoustic barriers are regularly installed along roadways, thoroughfares, and railway lines exposed to heavy motor vehicle traffic, in order to mitigate the resultant noise. However, if one of these panels is subject to a forceful impact, such as by being struck by an oncoming vehicle, the panel may shatter into multiple fragments, which may then fall onto the adjacent roadway in a hazardous manner. Accordingly, it is known to embed various forms of wires, cables or nets within the panel, which serve to contain any loose fragments formed upon impact. These embedded elements are typically made from a plastic material, such as monofilament polymer fibers. Ideally, the embedded elements also provide the panel with certain desirable properties, or maintain such properties that are already present in the panel, including: transparency, strength, ability to withstand inclement weather conditions, environmental friendliness, low cost, and ease of manufacture.
U.S. Pat. No. 4,029,037 to Hogan, entitled “Process for reinforcing plastic material and products therefrom”, is directed to a foamed plastic material with high tensile steel reinforcing elements, particularly suitable for the manufacture of sailing boat components. The high tensile steel elements are surface etched to each of the opposing surfaces of the foamed plastic core. The high tensile steel elements are preferably formed as wires, spaced in parallel, with a diameter of about 0.040 to 0.125 inches, having a yield strength of at least 200,000 psi, and located at a depth of at least 0.06 inches from the outermost surface.
U.S. Pat. No. 5,040,352 to Oberländer et al, entitled “Noise-protection elements of acrylic glass”, is directed to transparent acrylic panels for use as a sound barrier. The panel contains plastic threads, plastic bands or a plastic net, embedded approximately midway between the spaced parallel faces of the panel. The embedded threads or bands are arranged to run parallel to each other in one direction, or alternatively, in two perpendicular directions. If the acrylic glass breaks, the threads or bands expand and hold together the resulting fragments. The threads or bands are preferably monofilaments of polyamide or polypropylene, due to their low adhesion with acrylic glass.
U.S. Pat. No. 5,160,782 to Hickman, entitled “Wired glass”, is directed to glass formed with an embedded wire mesh, that acts as a reinforcement when the glass is struck or exposed to intense heat. The glass is made up of two spaced apart glazing panels, bonded together with an interlayer of adhesive material in which the wire mesh is embedded. The wires consist of a metallic core and an outer decorative coating that is colored, to provide the wires with a desired visual appearance.
U.S. Pat. No. 5,372,866 to Oberländer et al, entitled “Transparent plastic panels having bird protection, and use thereof as sound barriers”, is directed to transparent plastic panels suitable for noise barriers and which is intended to protect birds without disturbing the environment. The panels include embedded monofilament plastic fibers, to reduce fracturing or prevent fragmentation during breakage. The plastic fibers are formed with a high-contrast (i.e., having a low transmission ratio and different color from the background), such as using a black-dyed polyamide, enabling birds to recognize the transparent wall and avoid flying into it.
European Patent No. 0,559,075 to Müller, entitled “An appropriate noise protection element plate of acrylic glass”, is directed to an acrylic glass plate with embedded reinforcing strands for securing loose fragments in the plate surface. The strands are in the form of steel wire spirals, having a diameter less than the plate thickness, and arranged in parallel to one another. The interior of the steel wire spirals are either hollow or filled with a deformable medium.
U.S. Pat. No. 5,916,676 to Stasi, entitled “Antifragmentation plates based on acrylic polymers”, is directed to acrylic polymer plates to be used as barriers having anti-noise and anti-fragmentation properties. The plates contain a series of filaments of plastic material, positioned asymmetrically at a distance of between 20% and 35% of the total thickness of the plate, with respect to the surface opposite the surface subject to impact. The filaments preferably include monofilaments such as polyamide and polypropylene.
U.S. Pat. No. 6,641,903 to Schoela et al, entitled “Transparent plastic pane of acrylic glass, process for making the same and use of the same”, is directed to transparent plastic panes of acrylic glass suitable for noise protection walls and intended to not produce any splinters or loose fragments if the pane breaks. The pane includes internal plastic filaments embedded in the acrylic glass. The plastic filaments are made of monofilaments, such as polyamide or polypropylene. The plastic filaments are sized over a specified length (about 2 to 10 cm) at specified intervals (about 0.5 to 1.5 m). The sized filaments are at least partially coated with the residues of a sizing agent, which preferably contains a dissolved phenol-formaldehyde resin.
European Patent No. 1,936,035 to Japelj et al, entitled “Panels with antinoise and antifragmentation properties on the basis of acrylic glass, process for their preparation and use thereof”, is directed to acrylic glass (PMMA) panels suitable as antinoise elements for sound barriers on highways, bridges, viaducts, and the like. Reinforcing polymer monofilament fibers are embedded into the PMMA matrix in the form of a three-dimensional fiber entanglement. The fibers are oriented in all directions and distributed apparently uniformly in all directions. The polymer monofilament fibers may be polyethylene, polycarbonate, polyamide or polypropylene fibers, previously formed into a three-dimensional fiber entanglement that can retain its shape throughout a long period of time.
U.S. Pat. No. 7,665,574 to Schoela et al, entitled “Soundproofing restraining system”, discloses a sound deadening retention system made up of a transparent acrylic sheet with at least one embedded metal wire. A synthetic polymer layer is present between the surface of the metal wire and the transparent acrylic matrix, such that at least ninety percent of the metal wire surface is covered by the synthetic polymer layer. The polymer covered metal wires are preferably positioned with a degree of sag within the acrylic matrix, where the deviation is substantially perpendicular or substantially parallel to the sheet plane. The acrylic sheet may also include embedded synthetic polymer filaments for improving splinter retention. The retaining system may be used as a noise barrier on a bridge or multi-storey car park, where the puncturing of the barrier upon impact is prevented.